228 DEVELOPMENT AND HEREDITY. 



under peculiar and little known conditions male 

 characteristics may develop in the female, and female 

 characteristics may develop in the male. The dif- 

 ferent characteristics of the parents seem capable 

 of almost infinite variations of combinations, and 

 even the most distinguishing characteristics of the 

 two sexes may be combined in one individual. 



It is within the bounds of legitimate inference to 

 believe that inheritance among unicellular organisms 

 is fundamentally the same process as in the higher 

 organisms. Therefore we may assume that we are 

 right in our conclusion that the conjugation of two 

 individuals combines two potentialities of develop- 

 ment, — or combines two hereditary impulses into 

 one. But, as has been pointed out heretofore, the 

 hereditary impulse does not alone determine the 

 development, for the development is dependent on 

 the action of external forces or stimuli, which sus- 

 tain and guide its activity. The environment modi- 

 fies the hereditary impulse, and determines within 

 limits the intensity and direction of its development. 

 We may suppose the hereditary impulse to be made 

 up of two sets of potentialities of growth — one set 

 derived from each parent. Each of the two bits of 

 protoplasm which mingle to form an individual has 

 its associated co-ordinations of reactions ; which of 

 these reactions shall take effect depends upon the 



